BANGOR, Maine — The city’s interim police chief confirmed Wednesday that the Brewer Police Department has been asked to conduct the internal affairs aspect of its investigation into the alleged misconduct of a Bangor police detective accused of driving drunk while on duty.

Lt. Peter Arno, who came out of retirement to assume Bangor’s interim police chief post on Monday, said members of his department were conducting the investigation into the operating under the influence charge — the criminal part of the case.

The investigations were launched after Detective Erik Tall, a 15-year veteran of the Bangor Police Department, was issued a summons for OUI at 6:30 p.m. Oct. 3 at the Airport Mall on Union Street.

“A criminal investigation is just that, an investigation into an alleged crime, and the final disposition is heard by the court,” Arno said.

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An internal affairs investigation, on the other hand, is a noncriminal investigation into alleged misconduct by an employee, he said.

The two investigations must be kept separate as a matter of law, Arno said.

Asked whether the Bangor Police Department has a policy forbidding drinking while on the job, Arno said it does. “But there’s an even bigger policy — not to violate the law,” he said.

Fellow officers were tipped off that Tall had been drinking and went to the Airport Mall to check up on him, Penobscot District Attorney R. Christopher Almy said last week.

Tall, who was on the job at the time, has been on unpaid administrative leave since then. He could not be reached for comment on Wednesday.

Arno, who said Wednesday that he is still getting up to speed on the matter, said it was rare — but not unheard of — to have outside agencies investigate the activities of Bangor officers. In this case, however, he was still in retirement mode when the decision to do so was made.

“My guess is that obviously this is a sensitive issue and asking someone else to do it made some sense,” he said.

Arno declined to discuss any other specifics, adding that he was prohibited from doing so because it is a personnel matter.

He also declined to say when the investigations will be completed, but added, “We are absolutely not dragging our feet on this. We’re doing absolutely the best job we can to protect the public and the city.”

Arno said he would release a report after the investigations are completed and that he would inform the public of any final disciplinary action that might be taken, as he said is required by state law.

Though he, too, couldn’t divulge any details, Brewer Public Safety Director Perry Antone said Wednesday evening that he has one officer assigned to the internal investigation into Tall’s alleged misconduct.

The cost of Brewer’s assistance with the Bangor investigation is covered by a mutual aid agreement between the two departments, Antone said, adding that the two departments frequently share resources with and assist one another.